IPv6 – Airport Extreme update 7.6.3 breaks existing IPv6 tunnels

A few days ago I had an unexpected network problem. An IPv6 tunnel to tunnelbroker.net that had been up for months went down and wouldn’t restart. My tunnel endpoint is an Apple Airport Extreme base station (AEBS) that was originally running 7.6.1.

This all started when my ‘net connection died, IPv4 and IPv6 both just stopped working. I tracked it down to the AEBS. For some reason it just completely stopped passing any traffic at all. It’s done this twice before; it looks like the problem is uptime related. The AEBS seems to want a full power cycle about every 120-150 days of uptime.

Unfortunately, I also decided take the downtime as an opportunity to do the pending firmware update, to 7.6.3.

Apple changed the firmware to now require a valid IPv6 prefix in the “IPv6 Delegated Prefix” field in order to handle 6in4 tunnels. This field did not exist in earlier versions of the firmware, and was only added to the firmware around version 7.6 or so. At that time, existing configurations would still work, with no value in that field.

The 7.6.3 update requires a valid prefix, or the router will discard protocol-41 (6in4) packets from the other end of the tunnel.